Ink jet printing systems apply ink to a substrate. The inks are typically dyes and pigments in a fluid. The ink-receiving substrate can be comprised of a material or object. Most typically, the substrate is a flexible sheet that can be a paper, polymer or a composite of either type of material. The surface of the substrate and the ink are formulated to optimize the ink lay down.
Ink drops can be applied to the substrate by modulated deflection of a stream of ink (continuous) or by selective ejection from a drop generator (drop-on-demand). The drop-on-demand (DOD) systems eject ink using either a thermal pulse delivered by a resistor or a mechanical deflection of a cavity wall by a piezoelectric actuator. Ejection of the droplet is synchronized to motion of the substrate by a controller, which electrical signals to each ejector with appropriate timing to form an image.
U.S. Pat. No. 6,491,385 describes a continuous ink jet head and it's operation. An linear array of ejectors is disposed on a substrate. Each nozzle has a unique supply bore through the substrate. The supply bore ejects fluid through a nozzle in a membrane across the front surface of the supply bore. The membrane supports layers that form a pair of semi-circular resistive elements around each nozzle. Each resistor pair is pulsed to break the stream of fluid into discrete droplets. Asymmetric heating of the resistors can selectively direct the droplets into different pathways. A gutter can be used to filter out select droplets, providing a stream of selected droplets useful for printing. The modulated stream printing system requires significant additional apparatus to manage fluid flow.
Piezoelectric actuated heads use an electrically flexed membrane to pressurize a fluid-containing cavity. The membranes can be oriented in parallel or perpendicular to the ejection direction. U.S. Pat. No. 6,969,158 describes a piezoelectric drop-on-demand ink jet head having an electrically responsive piezo membrane which forces fluids through a nozzle. The ink jet head is formed of a stack of plates, which includes the piezoelectric membrane. The membranes require a large amount of surface area, and multiple rows of ejectors are arrayed in depth across the head. Ejectors are arranged across the printing direction at a pitch of 50 dpi and are arrayed in the printing direction 12 ejectors deep on an angle theta to form a head having an effective pitch of 600 dpi. Such heads are complex, requiring multiple layers that must be bonded together to form passages to the nozzle. The materials comprising the head and the structures do not lend themselves to incorporating semiconductor switching elements.
U.S. Pat. No. 6,926,284 discloses a drop-on-demand inkjet head permitting single-pass printing. A single pass print head comprises 12 linear array module assemblies that are attached to a common manifold/orifice plate assembly. Droplets are ejected from the orifice by twelve staggered linear array assemblies that support piezoelectric body assemblies to provide drop-on-demand ejection of ink through the orifice array. The piezoelectric system cannot pitch nozzles closely together; in the example, each swath module has a pitch of 50 dpi. The twelve array assemblies are necessary to provide 600 dpi resolution in a horizontally and vertically staggered fashion.
The orifice array on the plate can be a single two-dimensional array of orifices or a combination of orifices to form an array of nozzles. In the printing application, the orifices must be positioned such that the distance between orifices in adjacent line is at last an order of magnitude (more than ten times) the pitch between print lines. The assembly is quite complex, requiring many separate array assemblies to be attached to the orifice plate thorough the use of sub frames, stiffeners, clamp bar, washers and screws. It would be advantageous to provide a staggered array in a unitary assembly with an integral orifice plate. It would be useful for the spacing between nozzles to be less than an order of magnitude deeper than is disclosed in this patent.
U.S. Pat. No. 6,722,759 describes a common thermal drop-on-demand inkjet head structure. The drop generator consists of ink chamber, an inlet to the ink chamber, a nozzle to direct the drop out of the cavity and a resistive element for creating an ink ejecting bubble. Linear arrays of drop generators are positioned on either side of an ink feed slot. Two linear arrays are fed by a common ink feed slot. Ink from the slot passes through a flow restricting ink channels to the ink chamber. A heater resistor at the bottom of the ink chamber is energized to form a bubble in the chamber and eject a drop of ink through a nozzle in the top of the chamber. A matching set of transistors is formed adjacent to each resistor to provide a three-terminal switching device to each resistor. Sets of traces are provided adjacent to the transistors to provide power, power return and switching logic to each transistor. The structure limits nozzles to be placed in linear rows on either side of the ink jet supply slot. The patent uses both power supply and return lines, increasing the complexity of the device.
U.S. Pat. No. 5,134,425 discloses a passive two-dimensional array of heater resistors. The structure and arrangement of the droplet generators is not disclosed. The patent discloses the problem of power cross talk between resistors in two dimensional arrays of heater resistors. Voltages firing a resistor also apply partial voltages across unfired resistors. The parasitic voltage increases as the number of rows is increased to a maximum of 5 rows. The patent applies partial voltages on certain lines to reduce the voltage cross talk. The partial energy does not eject a droplet, but maintains a common elevated temperature for both fired and unfired nozzles. Passive matrix arrays of resistors are limited in the depth of the array because of the parasitic resistance. The patent suggests that the number of rows is limited to less than five rows.
U.S. Pat. No. 6,921,156 discloses forming inkjet heads on non-silicon flat-panel substrates. Thin film transistors are coupled to an array of ink jet drop generators. The monolithic substrate is described as being made of any suitable material (preferably having a low coefficient of expansion) and discloses a preferred embodiment of being ceramic. The device is multiplexed driven using flip chip devices bonded to conductors using solder. A single ink feed channel supplies two rows of nozzles. The resistors and chambers are formed using thin film processes. Multiple feedholes can supply each ejector from a single, common manifold for the two rows of ejectors. Reference to the thin film transistors on the substrate is limited, describing them as driving the resistors. The thin-film devices are formed over barrier and/or smoothing layers to isolate the thin-film devices from the substrate.
It would be useful to have a structure for an inkjet head that dispersed the nozzles in an array structure useful for high-speed printing. It would be useful to disperse ejectors in more than two columns. It would be useful for ejector arrays with a large number of rows to not have parasitic resistance.